Conventional antibody production methods typically consisted of immunizing an animal to obtain polyclonal antibodies from serum, or alternatively, immunizing a mouse or rat, isolating antibody-producing cells and obtaining monoclonal antibodies from a hybridoma established by cell fusion with a myeloma. Since these methods use live animals, the procedures are complicated and require considerable time and cost.
On the other hand, DT40 cells—a chicken B cell line—spontaneously cause mutation of antibody genes during culture and produce a diverse antibody repertoire.
Although there are reports on cells that produce antibodies having the desired specificity through physical adsorption onto an antigen obtained from a DT40 cell group during culture (see, for example, Patent Document 1, Patent Document 2 and Non-Patent Document 1), the accuracy of this method is low and requires considerable time and cost, similar to conventional methods.
Since the chicken B cell line DT40 and certain types of human or mouse B cell lines retain the ability to spontaneously cause mutation of their antibody genes during culture, a diverse repertoire of antibody genes is accumulated in such cultured cell populations. If it were possible to efficiently screen for B cells expressing a desired antibody from among these cells, it would be possible to establish an efficient antibody production method that uses cultured cells rather than animals. Such a method would become an important fundamental technology for producing antibodies in vitro.
In vitro antibody production methods are superior in that they are able to overcome several inevitable restrictions placed on in vivo antibody production methods using living organisms. For example, although it is difficult to obtain antibodies to self components, or to produce antibodies by immunizing with highly toxic antigens with in vivo production systems, these can be accomplished with in vitro systems.
Since the incidence of cells producing a desired antibody is predicted to be extremely low in the cultured B cells used in the present invention, it is virtually impossible to take out the individual cells and test their antibody production ability. Typically, the method referred to as “panning”, in which an antigen is immobilized onto a certain type of support and cells bound to the support are separated from unbound cells, or methods using a cell sorter are used to separate cells. However, to take out the less frequently occurring cells, the selection has to be performed repeatedly requiring both time and labor while the success rate is not necessarily high.    [Patent Document 1] Japanese Patent Kohyo Publication No. (JP-A) 2005-503826 (unexamined Japanese national phase publication corresponding to a non-Japanese international publication)    [Patent Document 2] Japanese Patent Kohyo Publication No. (JP-A) 2005-507241 (unexamined Japanese national phase publication corresponding to a non-Japanese international publication)    [Non-Patent Document 1] Cumbers, S. J. et al., Nature Biotechnology, 20:1129-1134 (2002)    [Non-Patent Document 2] Liu, X. et al., Journal of Virology, 77:2105-2115 (2003)    [Non-Patent Document 3] Li, X., Manley, J. L., Cell, 122:365-378 (2005)